The Prophet (peace and blessings of Allaah be upon him) also explained the reward earned by the one who says salaam, as was reported by al-Nisaa’i in ‘Aml al-yawm wa’l-laylah (368) and al-Bukhaari in al-Adab al-Mufrad (586) and by Ibn Hibban (493). They reported from Abu Hurayrah (may Allaah be pleased with him) that a man passed by the Messenger of Allaah (peace and blessings of Allaah be upon him) whilst he was sitting with some others, and said “Salaam ‘alaykum (peace be upon you).” The Prophet (peace and blessings of Allaah be upon him) said, “[He will have] ten hasanaat (rewards).” Another man passed by and said “Salaam ‘alaykum wa rahmat-Allaah (peace be upon you and the mercy of Allaah).” The Prophet (peace and blessings of Allaah be upon him) said, “[He will have] twenty hasanaat.” Another man passed by and said “Salaam ‘alaykum wa rahmat-Allaahi wa barakaatuhu (peace be upon you and the mercy of Allaah and His blessings).” The Prophet (peace and blessings of Allaah be upon him) said, “[He will have] thirty hasanaat.”
The Islamic greeting has been shown in the sunnah and Qur'an. Giving "salaam" is the right of a Muslim, either to give or to receive it. It is obligatory to return the salaam, or for one person among a group to reply to it.
When those who believe in Our Ayat (proofs, evidence, verses, lessons, signs, revelations, etc.) come to you, say: "Salamun 'Alaikum" (peace be on you); your Lord has written (prescribed) Mercy for Himself, so that if any of you does evil in ignorance, and thereafter repents and does righteous good deeds (by obeying Allah), then surely, He is Oft-Forgiving, Most Merciful.